Australian Patent Application No. 2006201223 discloses a known type of livestock head gate that employs an overhead guide shaft on which two doors are movably carried by respective roller carriages at the top ends of the doors so that rolling movement of the two doors toward one another when an animals neck is present in the animal-receiving opening of the gate will force the doors against the opposing sides of the animal's neck to secure the animals head in a generally stationary position.
In existing head gates of this type, the doors are automatically locked in place by a respective spring-loaded locking device installed in the roller carriage at the upper end of each door. The roller carriage features a housing in the form of a U-shaped channel with two side walls standing upward from a flat horizontal bottom wall. The guide shaft passes longitudinally through this channel-shaped housing between the side walls thereof and above the bottom wall thereof. Near each end of the channel, a set of two rollers engage the topside and underside of the guide shaft for rolling movement of the carriage horizontally along the guide shaft.
The existing locking device features a single locking plate that resides between the side walls of the carriage housing and that features a through-hole by which the guide shaft passes horizontally through the locking plate. A spring plate projects outwardly from the locking plate on one side thereof at a location below the through-hole and the guide shaft passing therethrough. A dowel spanning across the top end of the locking plate is seated in a pair of notched cutouts in the top edges of the carriage's vertical side walls, and a lower end of the locking plate hangs between a pair of positioning pins that cross horizontally through the side walls of the carriage housing just above the bottom wall thereof.
A coiled compression spring is disposed between the bottom wall of the carriage housing and the underside of the spring plate, whereby this spring biases the locking plate out of a vertical orientation into a tilted orientation leaning away from the spring loaded side of the lock plate. This tilted position locks the roller carriage at its current position on the guide shaft by causing the perimeter edge of the locking plate's through-hole to frictionally bite against the periphery of the guide shaft. Being spring loaded into this tilted locking position, the locking plate will automatically lock the roller carriage at any given position, until a lock-release lever is used to push the top-end dowel of the locking plate toward the spring loaded side thereof, thereby forcing the locking plate to a vertically upright orientation withdrawing the perimeter edge of the locking plate's through-hole out of its frictionally biting engagement with the guide shaft.
Applicant has found that there is a desire to improve on the existing locking devices for livestock head gates of this type.